【作者】 黄文新；

【导师】 文梓芸；

【作者基本信息】 华南理工大学 ， 材料学， 2011， 博士

【摘要】 地铁工程是国家级重大工程,对混凝土结构耐久性要求很高,一般设计使用寿命为100年。混凝土作为地铁工程用量最大的材料,材料的耐久性能对混凝土结构耐久性有着极大的影响;同时由于工程的特殊性,地铁混凝土处于潮湿和地下水流经的环境中,不仅遭受着比地面更严重的碳化环境和地下水的压力渗透作用,而且还受到地下水中存在的各种腐蚀性介质的侵蚀,同时还受荷载、列车振动、杂散电流等影响,在很大程度上加剧了对混凝土的侵蚀作用。因此,相对于其它建设工程,地铁混凝土由于遭受侵蚀而导致混凝土耐久性受影响的问题显得特别突出,直接关系到地铁混凝土结构的正常安全运行和使用年限,对地铁混凝土结构在各（多）因素作用下的抗侵蚀耐久性进行全面系统的研究,具有重要的理论意义和实践价值。本文以广州地铁工程混凝土为研究对象,率先在国内开展地铁工程混凝土在各（多）因素作用下的抗侵蚀耐久性的全面系统研究。首先,对地铁工程混凝土的侵蚀环境和侵蚀情况现状进行了现场调研,对实际工程混凝土使用的原材料和配合比进行了分析及对混凝土的耐久性能进行了常规性试验研究。然后,进一步采用模拟及加速试验方法,对地铁混凝土的抗碳化侵蚀、抗地下水溶蚀、抗Cl^-、SO₄^2-离子侵蚀,以及在杂散电流、荷载的复合因素作用下的侵蚀进行了深入系统的研究,在此基础上完成了地铁工程混凝土耐侵蚀性评价与建议。广州地铁工程混凝土侵蚀环境和侵蚀情况现状现场调研表明,地铁各线路沿线地下水对混凝土结构具有腐蚀性的比例为7.57%²8.87%,以侵蚀性CO₂的腐蚀所占比例最多,影响最大;对钢筋混凝土结构中钢筋具有腐蚀性的比例各线路均在50%以上,最高达80%左右,腐蚀因素以Cl^-的单因素腐蚀为主,Cl^-与SO₄^2-的双因素腐蚀占腐蚀水样的20%左右。地铁站厅、站台的碳化环境较地面稍严重,隧道内的碳化环境更为严重。在混凝土管片的预留孔、拼装缝,道床与二次衬砌混凝土的施工缝层面,混凝土现浇衬砌的施工缝、构造缝等位置容易出现渗漏溶出现象,由于各种原因导致的混凝土裂缝处渗漏也较严重,这是对地铁混凝土耐侵蚀性危害最大的一种形式,也是最为普遍的一种现象。对实际工程混凝土的质量调研和试验研究表明,除超过一半的砂样可能有潜在碱活性危害外,用于广州地铁工程的其它混凝土原材料质量状况良好;11家搅拌站供应广州地铁工程的C30P8同等级混凝土由于原材料、配合比、生产工艺的不同,混凝土各项耐久性能均有较大差异:抗渗性能优良,28d电通量在650¹360C之间,抗硫酸盐侵蚀系数在0.88¹.18之间,碳化深度从14mm到25mm不等,钢筋锈蚀失重率在0.06%⁰.25%之间,相互间差异较大,以电通量小于1000C,抗蚀系数在1.0¹.1之间,抗硫酸盐等级为“中”,碳化深度小于18mm的混凝土居多;存在电通量大于1000C,抗蚀系数<1.0,抗硫酸盐等级为“低”,碳化深度大于20mm的混凝土,不利于混凝土的耐久性。采用加速试验方法研究了地铁混凝土的抗碳化侵蚀和抗地下水溶蚀性能,运用模型相似理论,得到基于28天碳化结果的寿命预测公式: t_p=λ_tt_m=28（X_p/λ_aX_m）²/365说明混凝土碳化寿命与钢筋保护层厚度XP,28天标准碳化深度Xm相关,实际钢筋保护层厚度影响最大。11家搅拌站混凝土抗碳化耐久寿命从94年到312年不等,差异较大。根据试验结果并参考相关文献,得出混凝土抗渗漏溶蚀安全使用年限公式: T=0.1×VCa/Q（M-M₀）说明水渗漏溶蚀寿命与混凝土的水渗漏量Q,混凝土墙的CaO含量相关。若水渗漏量接近为零,则抗渗漏溶蚀寿命会无限延长。以石灰浸出量达到10%为临界状态,实测广州地铁混凝土某裂缝处日渗漏量为1000ml,由试验结果计算,得出地铁混凝土抗地下水溶蚀性能基本能满足100年的耐久性要求。采用模拟及加速试验方法深入研究了地铁混凝土抗地下水中Cl^-离子、SO₄^2-离子侵蚀性能,对10d¹80d渗透进混凝土中的Cl^-离子含量的测定结果进行曲线拟合,拟合方程为cj=atb。研究结果表明:提高温度使得乘数a增大;而干湿交替下使拟合方程的幂指数b增大;增大配制水溶液中氯离子的浓度对拟合方程的乘数a和幂指数b会同时产生影响,从而得出采用干湿交替养护,并适当提高配制水溶液中腐蚀离子的浓度,是研究Cl^-离子腐蚀的较好的加速试验方法。Cl^-+SO₄^2-双因素腐蚀下,渗透进混凝土中的有效Cl^-=Cl^-+SO₄^2-×0.25,试验表明,这个含量高于Cl^-离子单因素作用下渗透进混凝土中的Cl^-含量,即SO₄^2-离子的存在对钢筋锈蚀有加速作用。以混凝土中氯离子含量为水泥质量的0.1%为临界值,当地下水中氯离子含量为350.58mg/L（腐蚀等级为弱）时,对实际处于干湿交替环境中的地铁工程混凝土,渗透进入的氯离子含量拟合方程为:c j = 0. 01356t^0.20962,达到临界值需要37.8a,混凝土抗氯离子侵蚀的耐久性远低于设计要求;当地下水中氯离子含量为7203mg/L（腐蚀等级为强）,同时存在2805mg/L的SO₄^2-离子时,对实际处于长期浸水环境中的地铁工程混凝土,渗透进入的Cl^-+SO₄^2-×0.25含量拟合方程为: cj = 0. 02608t^0.30291,达到临界值仅需约90d,故对个别腐蚀严重部位应采取特殊防腐蚀措施。探讨了杂散电流对地铁混凝土抗溶蚀及抗地下水中Cl^-离子、SO₄^2-离子侵蚀性能的影响。假定混凝土中CaO溶出量与电流密度成正比,当地铁杂散电流为60mA/m2时,混凝土的抗溶蚀耐久寿命比单纯抗地下水溶蚀的耐久寿命缩短了约30%,杂散电流的存在加速了混凝土的溶蚀。与单纯地下水腐蚀作用相比,复合了杂散电流作用后,不仅加速了腐蚀离子的侵入速率,侵入混凝土内的自由氯离子和硫酸根离子含量显著增加;而且改变了腐蚀离子在混凝土中的分布状态,Cl^-离子在钢筋附近富集,从而显著加剧了混凝土中钢筋的锈蚀速率;增加腐蚀离子浓度对钢筋锈蚀的加速作用大于增加电流密度。研究了弯曲荷载和SO₄^2-、Cl^-离子共同作用下混凝土的抗侵蚀性能。在弯曲应力下,纯弯区拉应力层受荷载破坏最严重,使外部的SO₄^2-、Cl^-离子更容易向混凝土内部扩散,渗透进入混凝土中的SO₄^2-、Cl^-离子量最大,Ca2+含量被减少,从而使钢筋的锈蚀作用加速,短龄期已观察到钢筋的力学性能有所下降。至60d龄期,由于SO₄^2-、Cl^-离子反应生成的钙矾石和氯铝酸盐填充微小孔隙使结构致密而使混凝土的强度有所增大,但这些新产物在短时间内的裂缝愈合作用和增强作用并不足以减少它们对钢筋腐蚀的影响。荷载作用下,孔的周围应力集中,致使一些微孔扩展而形成大孔,混凝土的最可几孔径增大。所以,应力腐蚀对混凝土的影响重点在于使钢筋的锈蚀速度加快,其影响虽不及杂散电流,但是比单纯地下水腐蚀更厉害。在上述研究基础上,对广州地铁混凝土结构耐久性做了整体论的评价。广州地铁混凝土使用的原材料整体上质量情况良好,混凝土质量标准检验全部合格,配合比基本上合理,今后重点是解决材料的质量稳定性和施工的质量均匀性,从耐久性高度追求更严格的、更科学的配合比和更好的施工质量。认为本研究的实验室结果可以反映广州地铁混凝土结构主体的耐久性演变规律和可能的服役寿命;同时认为本研究在已建工程的实地勘察中发现的多种缺陷真实地反映了影响广州地铁混凝土结构耐久性的薄弱环节,如果不能妥善处理和大力防治,可能会成为影响地铁工程耐久寿命及安全性的关键问题。最后提出了提高广州地铁混凝土结构耐久性的措施建议和改进混凝土结构耐久性试验方法的建议。更多还原

【Abstract】 Being the State key project, metro engineering has a high demand for the durability of concrete structure whose designed service-life is about 100 years. Meanwhile, concrete is the biggest amount component material for subway engineering, its durability has great influence on that of concrete structure. And the particularity of metro environment is that the concrete structure is in a moist and groundwater flowing surroundings, in which it not only suffer, compared with on the ground, more serious carbonization attack and the action of groundwater pressure osmosis, but also was subjected to the attack of various corrosive medium existed in the groundwater and at the same time, the influence of loading, the vibration of running train and the stray current etc, all of which largely increased the concrete corrosion. In comparison with the other construction projects, the problem of concrete anti-corrosion durability for metro engineering is particularly prominent, which directly affects the normal safety operation and service life of metro system. So it is of important theoretical and practical value to comprehensively study the durability of metro concrete on erosion resistance in many factors.Taking GZ metro engineering as the research object, this paper takes the lead of the domestic in comprehensively studying the durability of metro engineering concrete structure in various factors and particularly in corrosion resistance. Firstly, a site investigation on the corrosion condition and situation of metro concrete engineering, an analysis on the raw materials and mix proportion of metro engineering concrete were carried out and a canonical experimental study on the durability of metro concrete was executed. Then,a further research on the resistance of carbonation and corrosive CO₂ attack, the groundwater dissolving corrosion, the corrosion of ions (Cl^-、SO₄^2-), and the erosion under the composite action of stray electric current and loading by using simulative experiment method designed particularly were realized. On the basis of these, a comprehensive evaluation on the concrete structure durability of GZ metro was presented and a set of suggestion for improving the anti-corrosion durability of metro project is completed.From the investigation in site on the corrosion condition and situation of metro concrete structure, it is demonstrated that 7.57%-28.87% of groundwater samples along with the metro line is corrosive to the concrete structure, of which, the corrosive CO₂ has the maximum ratio and the most important effects. Among every line of GZ metro, the average proportion of groundwater samples that have corrosive effect to the steel of reinforcement concrete is all more than 50%, the maximum is about 80%, the single corrosion factor of steel is mainly Cl^- ion, the composite corrosive factor of Cl^-and SO₄^2- consist of 20% of groundwater samples. Carbonation attack is slightly more serious in metro stations halls and platforms than on the ground, and is even much more serious in the tunnels. It is easy to find water leakage in the pre-embeded holes and joints of the prefabrication pipe sections, the construction joints between the track bed and the second lining concrete, the construction joints of the mine tunneling method concrete. There also exist serious leakage in the concrete cracks induced by various reasons, all of these are found to be the most harmful and popular way to destroy the corrosion resistance of the metro concrete.By the quality investigation and experimental durability detection of the practical metro engineering concrete, it was indicated that the quality of the raw materials used in metro engineering was well qualified, except that more than an half of sand samples have the latent alkali activity. The C30P8 concretes which were supplied by the 11 concrete companies varied in their durability performance because of the differences of raw materials, mix proportion and manufactured process: The anti-water-penetration performance of the concretes are all excellent, but the electric flux of 28d concrete samples varies among 650-1360C and the anti-vitriol corrosion coefficient ranges over 0.88-1.18, showing that the mutual differences between different companies are great. Most concretes have the 28d electric flux less than 1000C, the anti-vitriol corrosion coefficient being between 1.0-1.1 and the grade of the anti-vitriol corrosion bein“gmedium”. But, there are some concretes with low durability level, of which the 28d electric flux is greater than 1000C, the anti-vitriol corrosion coefficient is less than 1.0, the grade of anti-vitriol corrosion is low.Through a set of accelerated test methods, the resistance to carbonation and groundwater dissolving corrosion of the metro concrete was studied. By the use of model similarity theory, the service-life prediction equation of concrete carbonation based on the data of 28 days was obtained: t_p=λ_tt_m=28（X_p/λ_aX_m）²/365It is showed that the carbonation service-life is related to the thickness of reinforcement cover and the 28d standard carbonation depth of the concrete, practically, strongly relating to the former. The service-life prediction results among 11 concrete companies were quite different, varying from 94 years to 312 years.Taking the CaO leaching amount of 10% as the critical state of service life and the measured leakage amount per day at a certain crack of GZ metro concrete 1000ml as a parameter, the anti-seepage-corrosion safe life of the concretes, deduced by the accelerated test results, would be calculated as follow: T=0.1×VCa/Q（M-M₀）It is showed that the water corrosion service life is related to the percolating water amount and the total CaO content in the concrete. If percolating water speed tend to zero, the water corrosion service life would approach to infinite. With calculating from the experimental results, it can be concluded that the anti-seepage-corrosion performance of the concretes meets basically the requirements of 100-year durability.Through simulating and accelerating test methods, the corrosion resistance of the metro concrete to Cl^- ion, SO₄^2- ion in the groundwater was studied deeply. The fitted equation of penetration amount of Cl^- ion into concrete during 10d¹80d is cj=atb. The test results showed that: the multiplier“a”became larger when temperature rose, the exponent b increased when alternate wetting and drying curing was used, augmenting the concentration of chloride ion would aggrandize the multiplier a and the exponent b simultaneously. Therefore, the alternate wetting and drying and higher concentration of chloride ions curing is a good accelerated test method for studying Cl^- ions corrosion. In the condition of Cl^-+SO₄^2- multiple corrosion, the average penetration amount of Cl^-+SO₄^2-×0.25 （effective Cl^- ions content） was higher than the average penetration amount of Cl^- ion in the condition of Cl^- ion single factor corrosion, which indicates that the existence of SO₄^2- ion accelerated the steel corrosion. Taking 0.1% content of chloride over cement mass as the critical value of steel corrosion, when the measured chloride content in groundwater was 350.58mg/L （“weak”corrosion grade） and the condition of metro was in alternate wetting and drying, the regression equation for chloride ion content, Cj, infiltrating into concrete is: c j = 0 .01356t^0.20962, and attaining this critical value needed only 37.8a, so, the chloride resistance of concrete was far lower than the design requirements. When the measured Cl^- ion and SO₄^2- ions content in groundwater was 7203mg/L （“strong”corrosion grade） and 2805mg/L respectively, and the metro concrete was immersed in groundwater in long-term, the fitted regression equation of Cl^-+SO₄^2-×0.25 was c j = 0 .02608t^0.30291, and attaining this critical value needed only 90d. Apparently, a special anti-corrosion measures should be taken for the individual parts under serious corrosion condition.The influence of stray current on the dissolving corrosion resistance and Cl^- ion and SO₄^2- ion corrosion resistance of the metro concrete was explored. Assuming that the amount of the dissolving CaO was proportional to the current density in concrete and the stray current of the metro was 60mA/m2, it is demonstrated that the service life of metro concrete reduced by 20% compared with that of no stray current only, so the presence of stray current obviously accelerated the ions corrosion. Compared with groundwater corrosion, the stray current not only increased the invasion rate of ion , significantly increased the content of free chloride ions and sulfate ion into concrete, but also changed the distribution state in the concrete of the corrosion ions, Cl^- ion concentrating near the steel, thus significantly increasing the corrosion rate of steel in concrete. Meanwhile, increasing the concentration of the corrosion ions had the greater influence on the steel corrosion than increasing the current density.The anti-corrosion power of metro concrete against the combination action of bending loading and SO₄^2-, Cl^- ion in the groundwater was studied. It is showed that stretching strength caused by the bending stress of loading led micro-fissure to form and extend and outside SO₄^2-, Cl^- ion to penetrate inside more easily and more concentrating in the pure tension stress area, oppositely, the content of Ca2+ ion to decrease, all of which would accelerate the rusting of reinforcement. The mechanic performances of steel bar had been found to descend. The concrete structure was tested to be densified and the strength increased slightly because of the formation of ettringite to fill the fissures, and the existing of Cl^- ion in the structure weakened the densification result. But, this kind of densification and strengthening is insufficient to compensate the effect of attacking of Cl^- and SO₄^2- ions to the reinforcement. The loading action led the stress focusing around the holes and some micro-fissures to extend to become big holes, the most probable bore diameter being increase. Therefore, it is obviously that the important influence of stress corrosion on concrete lies in accelelating the rusting of reinforcement of concrete, which might be milder than that of stray current but graver than that of the erosion of groundwater. Based on the above-mentioned research on durability, a holistic evaluation is made on the durability of concrete structure in GZ metro. The raw materials used for Guangzhou metro concrete are qualified as a whole, the examination of concrete quality all meets the requirements of standard, and the mix proportion is basically reasonable. It is the key point from now on to settle the quality stability of raw materials and the quality uniformity of construction structure, to pursue stricter and scientific mix proportion and the more excellent construction quality aiming to the level of durability. The laboratory research result in this toFig is considered to reflect the durability regulation and possible service life of the concrete main body structure of GZ metro; it is also considered that various defects found through the investigation of built project in site truly reflect the weak link of the durability of GZ metro concrete structure in GZ metro. If they can’t be handled carefully and cured strongly, they may become the key problems which influence the durability life and safety of the metro engineering. At the last, some measure suggestions are put forward to improve the durability performance of the concrete structure in GZ metro and certain proposals about the experimental method for concrete durability are also presented.更多还原